The most advanced development of the classic bulldozer is the front-end tractor shovel. This machine is also called a shovel dozer, a dozer shovel, a tractor loader, an end loader, a front loader, or just a loader. It is used for digging, loading, rough grading and limited hauling. A typical front loader includes a support frame often mounted on a tractor, a hydraulic system, a pair of push or lift arms--sometimes called a boom--hinged to the top of the support frame, a tractor-width bucket hinged to the front of the lift arms, and a pair of dump arms hinged to both of the lift arms and to the bucket. Buckets range in size from one to four and one half yards. Wheeled tractors have both smaller and larger sized buckets from five cubic feet to over twenty yards.
A standard method of digging with a tractor loader is to use low gear to force the bucket into the bank toe at ground level. When the resistance slows the tractor, the bucket is rolled back gradually and hoisted, while crowding of the tractor is continued. Rolling back the bucket as it rises in the bank increases the cutting efficiency by aligning the digging edge with its upward movement. By retracting the bucket for a thinner slice, the bucket's own suction and crowding by the tractor, tend to make the cut thicker. The proper balance among these forces varies with the machine, the bank and the position and momentum of the bucket. It is the responsibility of the machinery operator's (hereinafter also referred to as the "operator") to so balance these forces so that he will get a good bucket load in a minimum time. This requires him to have a good "feel" for the position of the leading or digging edge of the bucket.
If the machine is driven head-on into the bank and gets under too great a load the bucket may remain stuck forcing the back end of the tractor to rise. Correcting for a better angle of attack to the bank wastes time and reduces the overall efficiency of the machine. Therefore, a bucket design which improves the operator's "feel" for the position of the digging edge and his bucket will by necessity improve the overall efficiency of the machine.
Most of the medium and large size loaders supported on rubber tires are on articulated, four wheel drive tractors. The loader bucket is on the front end section or frame. The lift arms are therefore shorter than on an ordinary tractor loader and consequently rise to a steeper angle for the same bucket height. The machinery operator controlling the bucket usually sits relatively high and forward on the front frame where he has a relatively good view of the rear end of the bucket. However, by being so far forward, the operator is exposed to a greater danger of objects falling off the back of the bucket. For this reason, a "spill guard" or "spill wall" is often installed at the rear end of the bucket. This, in turn, further limits the operator's view of the interior and leading edges of the bucket when the bucket is lowered.
Large buckets and standard size buckets with large spill-guards obscure the digging edge of the bucket from view. Frequently, it is extremely difficult for the operator to manipulate his machine to properly align the digging edge with the load to be picked up. Furthermore, it is often difficult for the operator to judge the amount of payload in the bucket unless material is forced over the top of the spill guard.
Thus, a bucket design which allows the operator to directly see the leading edges or the digging edge of the bucket is particularly desirable in that the operator will not have to interpolate for the exact position of the digging edge of the bucket.